Silver(I) nitrate adducts with bidentate 2-, 3- and 4-pyridyl phosphines. Solution 31P and [31P–109Ag] NMR studies of 1∶2 complexes and crystal structure of dimeric [{Ag(d2pype)(µ-d2pype)}2][NO3]2·2CH2Cl2 [d2pype = 1,2-bis(di-2-pyridylphosphino)ethane]

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Abstract
The 1∶2 complexes of silver(I) nitrate with 1,2-bis(di-n-pyridylphosphino)ethane (dnpype) for n = 2, 3 and 4 have been synthesized and solution properties characterized by NMR spectroscopy, including variable-temperature one-dimensional 31P-{1H}, two-dimensional [31P–31P] COSY and [31P–109Ag] HMQC NMR experiments. The 3-pyridyl (d3pype) and 4-pyridyl (d4pype) complexes exist as bis-chelated monomeric [Ag(d3pype)2]+ and [Ag(d4pype)2]+ while the 2-pyridyl (d2pype) complex forms an equilibrium mixture of monomeric [Ag(d2pype)2]+, dimeric [{Ag(d2pype)2}2]2+ and trimeric [{Ag(d2pype)2}3]3+ species in which the d2pype ligands co-ordinate in both bridging and chelated modes via the phosphorus atoms. The relative percentages of the species present are dependent on both temperature and solvent. Crystals of the 2-pyridyl complex obtained from CH2Cl2–Et2O solution have been shown by crystal structure determination to be the dimer [{Ag(d2pype)(µ-d2pype)}2][NO3]2·2CH2Cl2. Each silver ion is co-ordinated by one chelated and two bridging d2pype ligands forming a ten-membered ring in a double boat conformation. The pyridyl nitrogen atoms do not co-ordinate to the silver. The differences in solution behaviour of the three systems and the potential significance of these complexes to the antitumour properties of chelated 1∶2 silver(I) diphosphine complexes are discussed.

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